The present invention relates to reclosable plastic bags, and more particularly to a method and apparatus for joining closure members to a bag film web, and the reclosable bag film formed thereby.
Reclosable plastic bags typically include a bag film web portion and a closure member portion. The bag film web portion generally consists of a pair of opposed planar plastic sheets which are sealed on three sides to form a bag body. The closure member portion extends along the fourth side of the plastic sheets and includes a female (or groove) fastener profile and a male (or rib) fastener profile. The closure members can be interlocked by the consumer to form a sealed container, and disengaged to permit the consumer to gain access to the interior of the bag. An example of such a reclosable bag is the ZIPLOC.RTM. brand food storage bag manufactured by The Dow Chemical Company, the assignee of the instant invention.
One difficulty experienced by manufacturers of such reclosable bags involves the joining of the closure members to the bag film web portion. In order to produce a high-quality reclosable bag, care must be taken to ensure that the fastener elements are positioned properly on the bag film web. Further, there should be no wrinkles or creases in the area of the bag in which the fastener profiles and bag film web are joined.
Several approaches are described in the patent literature for forming reclosable bags. One approach has been to form the bag film web and the closure members in a single extrusion operation. See, e.g. Ansnit, U.S. Pat. Nos. 3,338,284; Behr, 3,852,386 (also assigned to the assignee of the instant invention), and Naito, Re. 29,208.
A second approach utilizes an adhesive, such as a strip of tape or glue, to join a closure member to a bag film web. For example, Ausnit U.S. Pat. No. 4,101,355 discloses a reclosable bag film forming process wherein a web and closure member are joined by a liquid adhesive which is supplied by an applicator having a nozzle. After the adhesive is applied, the web and closure members are pressed together by a presser roll and a backing roll. See also, Ausnit, U.S. Pat. No. 3,226,787.
A third approach involves the use of a pre-formed bag film web and a pre-formed closure member which are drawn from separate stock rolls. The bag film web and/or closure member are then heated and joined. For example, Howard, U.S. Pat. No. 3,846,209 discloses a method for producing a closure member-containing bag film wherein a pre-formed plastic film is fed from a stock roll into a sealing station. A separate closure strip from a second stock roll is also fed into the sealing station. In the sealing station, the closure strip and plastic film are welded together by a pair of heating bars.
A fourth approach wherein a pre-formed bag film web is drawn from a supply roll, and then joined to a relatively freshly extruded closure member, is disclosed in several patents. For example, Noguchi, U.S. Pat. No. 3,904,468 discloses a method of making a reclosable bag film wherein a web of bag film material is unwound from a stock roll and then transferred to a heating station having a heating roll on which the film is heated to a desired temperature. The film is then transferred to a heated joining roll wherein the film is joined to the freshly extruded fastener profile strips. See also, Takahashi, U.S. Pat. Nos. 4,279,677; and Ferrell, 4,582,549.
Another variation on this fourth approach is disclosed in Yano, U.S. Pat. No. 4,555,282. Yano discloses a method of bonding a closure member to a bag film web wherein a closure member having a base portion and a fastener profile portion is extruded shortly before being bonded to a bag film web. Intermediate the extrusion of the closure member and its joinder to the bag film web, the fastener profile portion of the closure member is cooled (and thereby solidified and stabilized) while the base portion is left heated (and thereby remains thermoplastic) when the closure member is joined to the film. Kamp, U.S. Pat. No. 4,306,924 discloses another variation on this fourth approach wherein the film web is extruded on to a casting roll to join an already formed closure member.
A fifth approach involves the extrusion of a bag film web and a closure member in close proximity to each other, and the joinder of the bag film web and closure member to each other shortly after extrusion. For example, Kamp U.S. Pat. No. 4,428,788 discloses a method for forming a reclosable bag wherein a film, a tape, and a closure member are extruded by three separate dies. The film, tape and closure member dies are positioned so that the film, tape and closure members contact each other while still at a temperature of above 200.degree. F. A chill roll is provided for cooling the film, tape and closure members. Sutrina et al, U.S. Pat. No. 4,295,915, which is assigned to the same assignee as the instant invention, discloses to an apparatus for forming a reclosable bag film wherein a fastener profile and its base strip are extruded integrally, and then joined to a film web. The die for extruding the bag film web is disposed adjacent to the fastener die block so that the fastener profile and bag film are joined shortly after both are extruded. See also Goto, U.S. Pat. Nos. 3,462,332 and Zieke, 4,522,678.
Although the above discussed patents all disclose various methods for forming reclosable bags, room for improvement exists in the fabrication of a reclosable bag which can be manufactured to consistently high quality standards. Accordingly, it is an object of the present invention to provide a method and apparatus which can produce high quality reclosable bag film webs consistently.